Finishing machines are used to perform finishing operations such as deburring, burnishing, descaling, cleaning and the like. Such machines include a movably mounted chamber and a drive system for vibrating the receptacle. Workpieces to be finished are loaded into the chamber together with finishing media. A finishing action is imparted to the workpieces by vibrating the chamber so that the mixture of workpieces and media is effectively maintained in a fluid or mobile state with smaller components of the mixture dispersed between larger components so that the larger components receive finishing treatment from the smaller components. Impulse forces imparted to the mixture not only cause repeated impacts among its components but also cause the mixture to chum in a predictable manner as a finishing process is carried out.
Two basic types of unbalanced-mass vibratory finishing machines are in common use. An earlier type of finishing machine such as that described in U.S. Pat. No. 4,228,619 to Anderson employs an elongate chamber which defines an elongate, trough-like finishing chamber extending in a substantially horizontal plane, and which is vibrated by rotating one or more eccentrically-weighted drive shafts about one or more substantially horizontally axes extending along the chamber. This type of machine is known in the art as a "tub machine".
Another, newer type of machine such as that described in U.S. Pat. No. 3,161,993 to Balz, uses a substantially toroidal-shaped chamber which defines an annular, trough-like finishing chamber extending in a generally horizontal plane, and which is vibrated by rotating an eccentrically-weighted drive shaft about a substantially vertical "center axis" located centrally of the chamber when the chamber is at rest. This type of machine is known in the art as a "bowl machine".
Both types of machines use inertial centrifugal vibrators (i.e. unbalanced mass type mechanisms) to provide vibrations excitation. It is important to be able to increase the amplitude of the vertical velocity vibrations in order to increase the intensity (i.e. velocity) of the finishing process. However, unbalanced-mass finishing machines are prone to a number of operational disadvantages.
First, when the machine power supply is turned off and braking is applied to the drive shaft, the large machine components rapidly lose their accumulated energy. When the rotation frequency of the drive mechanism coincide with the vibrations of the larger machine components on an elastic suspension there is a corresponding increase in the non-stationary vibratory load that acts on the floor or foundation of the building where the finishing machine is mounted. In order to avoid the horizontal displacement of the machine when it is turned off, it is necessary to secure the elastic suspension of the chamber to the heavy base which in turn significantly limits the intensity of the working vibrations of the machine and, consequently, the finishing intensity.
Generally, the amplitude of the transitional regime is known to increase with the increase of the amplitudes of the operational regime and with the increase of the polar moment of inertia of the unbalanced shaft. Therefore, in practice, in order to achieve an acceptably high amplitude of the operational vibrations in unbalanced-mass vibratory machines, the double amplitude of vibrations is limited (e.g. to between 4 and 8 millimeters), and the frequency of operational vibrations is increased (e.g. above 1200 rpm). However, such increases in frequency requires the rigidity of the chamber and the machine to be increased and accordingly the loads acting on the supports and the associated noise level increase as well.
Also, designers of both types of finishing machines have attempted to provide a simple and relatively inexpensive, yet reliable system which will enable a truly aggressive finishing action to be imparted to the contents of the chamber. A challenge facing the industry has been to provide an efficient bowl machine design which is capable of generating the type of large amplitude velocity vibrations needed to provide an aggressive finishing action, while minimizing the use of inordinately massive and costly machine components.
Accordingly, there is a need for an improved finishing assembly which provides aggressive finishing action while using a low-energy input drive system, which comprises relatively few parts, and which is durable and relatively inexpensive to manufacture.